Sheet feeding device

ABSTRACT

A sheet feeding device includes a feed roller consisting of a rigid roller and an elastic coating covering at least part of the feed roller. A sheet is placed between the pressing member and the feed roller and is pressed tightly by the pressing member. While the feed roller rotates, the sheet is fed by means of the friction between the sheet and the pressing member and between the sheet and the feed roller. The thickness of the elastic coating is preferably much less than the radius of the rigid roller, and is also preferably less than 0.5 millimeter.

FIELD OF THE INVENTION

[0001] The present invention relates to a sheet feeding device, especially relates to a sheet feeding device which has a thin elastic coating and feeds a sheet accurately. The present invention may be applied to a variety of facilities such as printers, facsimile machines, and photostat machines, etc.

BACKGROUND OF THE INVENTION

[0002] A sheet feeding device is generally equipped with a feed roller and a pressing member. A sheet is placed between the pressing member and the feed roller and is pressed tightly by the pressing member. While the feed roller rotates, the sheet is fed by means of the friction between the sheet and the feed roller and between the sheet and the pressing member. Traditionally, there are two kinds of prior arts, as shown in FIG. 1 and FIG. 2, for the sheet feeding devices.

[0003] Please refer to the prior art as shown in FIG. 1. A feed roller 10 includes a rigid roller 13 and a rubber coating 11 covering the rigid roller 13. When a sheet S is placed between the pressing member 12 and the feed roller 10 and is tightly pressed by a pressing member 12, the rubber coating 11 results in a deformed area N due to the excessive thickness of the rubber coating 11, usually more than 2 millimeters. Thus, the sheet S is fed to an inaccurately position because of the deformed area N. That is, when the feed roller 10 rotates for 360°, the displacement of the sheet S would not be equal to the circumference of the feed roller 10.

[0004]FIG. 2 illustrates another prior art in which a feed roller 20 includes a rigid roller 23 and a coating 21, with ceramic particles 29, covering the rigid roller 23. A sheet S is placed between a pressing member 22 and a feed roller 20 and is tightly pressed by the pressing member 22. When the feed roller 20 rotates in the direction C, as shown in FIG. 1, the sheet S is fed in the direction D accordingly. However, the fibers of the sheet tend to attach to the ceramic particles 29 of the coating 21. As a result, sufficient friction cannot be obtained and the sheet S can not be fed to the desired position accurately. In addition, in order to adjust the friction between the sheet S and the feed roller 20 and the friction between the sheet S and the pressing member, the distribution density of ceramic particles 29 on the coating 21 may need to be controlled. As such, the manufacturing cost of the sheet feeding device is increased, and the manufacturing process becomes more complicated.

[0005] As a result, the object of the present invention is to provide a sheet feeding device for solving the aforementioned problems such as improving the accuracy of feeding the sheet and reducing the cost of manufacturing.

SUMMARY OF THE INVENTION

[0006] The present invention reduces the thickness of an elastic coating on a feed roller. Therefore, it results not only in a decrease of the deformed area, as shown in the FIG. 1, but also in reduction of the manufacturing cost. In addition, the cost of the rubber coating is much lower than the cost of applying the ceramic particles to the feed roller. Further, the prior art as shown in FIG. 2 has an additional problem. The distribution density of the ceramic particles has to be controlled so as to adjust the friction between the sheet and the feed roller and the friction between the sheet and the pressing member, and thus the difficulty and cost of manufacturing is increased. Hence, the present invention provides a sheet feeding device with an easier manufacturing process and a lower cost, and easily solves the aforementioned problems.

[0007] According to the aforementioned object, the present invention provides a sheet feeding device including a feed roller consisting of a rigid roller and an elastic coating of a limited thickness covering the rigid roller. A sheet is placed between the feed roller and the pressing member and is pressed tightly by the pressing member. When the feed roller rotates, the sheet is fed by means of the friction between the sheet and the pressing member and between the sheet and the feed roller.

[0008] In order to illustrate the objects, the features, and the advantages of the present invention more clearly, the following preferred embodiments accompanied with the attached figures are introduced hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 and FIG. 2 illustrate enlarged cross-sectional views of two traditional sheet feeding devices;

[0010]FIG. 3 illustrates a preferred embodiment of the sheet feeding device according to the present invention;

[0011]FIG. 4A illustrates the side view of an embodiment of the sheet feeding device in accordance with the present invention; and

[0012]FIG. 4B illustrates the side view of another embodiment of the sheet feeding device in accordance with the present invention.

DETAIL DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENT

[0013] In order to reduce the manufacturing cost and to avoid the complicated process, the present invention provides a thin rubber coating covering a rigid roller to form a feed roller. A sheet is placed between the feed roller and the pressing member and is pressed tightly by the pressing member. When the feed roller rotates, the sheet is fed by means of the friction between the sheet and the pressing member and between the sheet and the feed roller.

[0014] Referring to FIG. 3, a sheet feeding device provided by the present invention includes a feed roller 30 and a pressing member 32. The feed roller 30 further consists of a rigid roller 33 and an elastic coating 31. Furthermore, the material of the elastic coating 31 is preferably rubber. A sheet S is placed between the feed roller 30 and the pressing member 32 and is pressed tightly by the pressing member 32. The friction coefficient between the sheet S and the feed roller 30 and the friction coefficient between the sheet S and the pressing member 32 are μ₁ and μ₂ respectively. While the feed roller 30 rotates in the direction C, the sheet S can be fed accurately in the direction D, as shown in FIG. 3, only if the friction coefficient μ₁ is greater than the friction coefficient μ₂.

[0015] In order to reach the accurate position while feeding the sheet S, the thickness T of the elastic coating 31 on the feed roller 30 is preferably much less than the radius of the rigid roller 33, and also preferably less than 1 millimeter, as shown in FIG. 3. Furthermore, when the thickness T of the elastic coating 31 is less than 0.5 millimeter, the deviation between the predetermined feeding position and the actual feeding position will be within ±0.02 millimeter.

[0016] According to the present invention, the feed roller can be coated in two different ways, as shown in FIG. 4A and FIG. 4B. FIG. 4A shows that the elastic coating 41 completely covers the surface of the rigid roller 43. On the other hand, in FIG. 4B, the rigid roller 43 is divided into few sections and the elastic coating 41 only covers on some of these sections. Though the feed roller 40 may be coated in two different ways, the function of the feed roller remains the same. The pressing member 42 and the feed roller 40 are adopted as the sheet feeding device to feed the sheet S.

[0017] In addition, it should be noted that all kinds of sheets, e.g. regular papers, coated papers, overhead projector sheets/films, and glossy papers/films, etc. can be adopted by the device of the present invention to achieve accurate sheet feeding.

[0018] Furthermore, the sheet feeding device of the present invention can be applied to a variety of facilities such as printers, facsimile machines, and photostat machines, etc.

[0019] Although only a few embodiments of the present invention have been described in detail herein, it should be understood that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given therein, but may be modified within the scope of the appended claims. 

What is claimed is:
 1. A sheet feeding device, comprising: a feed roller comprising a rigid roller and an elastic coating covering at least part of said rigid roller, the thickness of said elastic coating being substantially less than 1 millimeter, and said feed roller rotating to feed a sheet; and a pressing member, said sheet being placed between said pressing member and said feed roller, and said sheet being pressed tightly by said pressing member.
 2. The sheet feeding device of claim 1, wherein the thickness of said elastic coating is substantially less than 0.5 millimeter.
 3. The sheet feeding device of claim 1, wherein said elastic coating is a rubber coating.
 4. The sheet feeding device of claim 3, wherein the thickness of said rubber coating is substantially less than 1 millimeter.
 5. The sheet feeding device of claim 4, wherein the thickness of said rubber coating is substantially less than 0.5 millimeter.
 6. A sheet feeding device built in a printer for feeding a sheet, comprising: a feed roller comprising a rigid roller and an elastic coating covering part of said rigid roller, the thickness of said elastic coating being less than a specific thickness, and said specific thickness being much less than the radius of said rigid roller; and a pressing member operating in conjunction with said feed roller for feeding said sheet, and said sheet being placed between said pressing member and said rigid roller, and said sheet being pressed tightly by said pressing member.
 7. The sheet feeding device of claim 6, wherein said specific thickness is substantially 1 millimeter.
 8. The sheet feeding device of claim 6, wherein said specific thickness is substantially 0.5 millimeter.
 9. The sheet feeding device of claim 6, wherein the said elastic coating consists of rubber.
 10. A sheet feeding device built in a printer for feeding a sheet, comprising: a feed roller comprising a rigid roller and a rubber coating covering part of said rigid roller, and the thickness of said rubber coating being less than 1 millimeter; and a pressing member operating in conjunction with said feed roller for feeding said sheet, said sheet being placed between said pressing member and said rigid roller, and said sheet being pressed tightly by said pressing member.
 11. The sheet feeding device of claim 10, wherein the thickness of said rubber coating is substantially less than 0.5 millimeter. 